1. Field of the Invention
The present invention relates generally to sewing machine feed conversion apparatus, and more particularly, but not by way of limitation, to an apparatus for attachment to a sewing machine having a bottom workpiece feed mechanism and a top presser foot mechanism to convert the machine to one having a reverse-pivoted bottom workpiece feed mechanism, a top workpiece feed mechanism (which includes the conversion of the top presser foot mechanism to a workpiece feed foot mechanism), a top workpiece clamping mechanism and an adjustable hook throw mechanism whereby workpieces of extra thickness can be fed and sewn through the machine and whereby workpieces having designs which are to be matched at their seams can be more easily maintained in alignment and sewn and whereby workpieces can be sewn with variable amounts of thread throw.
2. Description of the Prior Art
Various sewing machine apparatus for both domestic use and commercial use have been developed. Generally, sewing machines intended for domestic use include bottom workpiece feed mechanisms. That is, there machines include a feed dog which is positioned in the work supporting surface of the machine and which is raised, moved in the direction of feed, lowered and moved in the opposite direction with each cycle of the needle. In domestic machines the raising and feed-direction movements of the feed dog occur while the needle is placed in non-sewing positions, whereas the lowering and reverse feed direction movements of the dog occur while the needle is placed to penetrate and stitch the workpiece. Such machines also include a presser foot mechanism for urging the workpiece being stitched against the work supporting surface so that the feed dog contacts the workpiece and moves it forward when the feed dog is raised and moved in the direction of feed.
Sewing machines intended for commercial use, on the other hand, generally include feed mechanisms which grip both the top and bottom surfaces of the workpiece whereby the workpiece can be of extra thickness but still be fed through the mechanism and stitched by the machine. Such top and bottom workpiece gripping feed mechanisms usually include a feed dog, similarly positioned below the workpiece as in the domestic machine but moved through the various positions at different times with respect to the position of the needle, and a feed foot mechanism, positioned above the workpiece and moved in timed relationship with the feed dog to advance the workpiece. In other words, the feed foot is lowered into contact with the top surface of the workpiece, the feed dog is raised into contact with the bottom surface of the workpiece, and then both are moved in the direction of feed so that the workpiece is advanced. The stitching of the workpiece also occurs during this time of the feed dog's raising and feed-direction movements. As will be noted, this is contrary to the timing of the domestic machines. Such simultaneous top and bottom workpiece gripping feed mechanisms make it possible for extra thick workpieces or multi-layered workpieces to be advanced and stitched by the machine. Having the feed foot mechanism converted from the top presser foot mechanism and having the converted mechanism and needle bar pivotally connected to the sewing machine makes it possible to better maintain the alignment of workpieces which have designs that are to be matched along the seams of the workpiece.
Additionally, sewing machines intended for commercial use may include mechanisms for adjustably controlling the amount of throw on the hook used to loop the needle-fed thread around the bobbin. This throw adjustability feature permits improved sewing capabilities over those exhibited by domestic-type, fixed-throw sewing machines.
Therefore, it is apparent that sewing machines intended for domestic use have the shortcoming of lacking the versatility possessed by a commercial sewing machine. Although sewing machines intended for commercial use may have the additional features, they have the shortcoming of generally being considerably more expensive than domestic sewing machines. Therefore, there is the need for relatively inexpensive conversion apparatus which can be attached to a domestic machine to convert it to one having capabilities of a commercial machine. Although a conversion apparatus has been proposed in the U.S. Pat. No. 3,952,675 issued to Thompson, it fails to disclose the various features of the conversion apparatus of the present invention.